1. Field of the Invention
The present invention relates to an arrester, and particularly, to an arrester in which a plurality of zinc oxide elements are laminated within a porcelain bushing or within a tank.
2. Description of the Prior Art
In conventional insulator type arresters, it was feared of bringing forth a phenomenon that when the surface of a porcelain bushing is locally unevenly contaminated, an excessive electrical stress is applied to a part of the zinc oxide elements for a long period of time whereby the zinc oxide elements are generated in heat, finally resulting in reckless running, as mentioned in S. Shirakawa et al.: DC and AC Contamination Characteristics of Two Staged Porcelain Type Surge Arresters, 10th ISH, Montreal, 1997.
That is to say, it was feared that when the zinc oxide elements are thermally unbalanced, a leaky current of the zinc oxide elements increases, whereby a temperature of the zinc oxide elements rapidly rises, resulting in thermally reckless running of the zinc oxide elements. Further, it was feared that when, in a state that a temperature of the zinc oxide elements rises, a large thunder surge or a frequent opening- and closing surge in a system is absorbed, the temperature of the zinc oxide elements assumes a state that exceeds a thermal balance of the zinc oxide elements (for example, the temperature of the zinc oxide elements exceeds approximately 200xc2x0 C.), whereby a leaky current of the zinc oxide elements abnormally increases, resulting in a high possibility of thermally reckless running.
The basic characteristics of zinc oxide elements for an arrester are evaluated by a terminal voltage of the zinc oxide elements in conductance of 1 mA and a thickness of the zinc oxide elements. In the prior art, the zinc oxide elements of approximately 200 V/mm have occupied a main stream.
In the insulator type arrester, higher performance attained by reduction in a limit voltage has been expected for improvement in protective level. However, since an insulator type arrester capable of suppressing a rise in temperature of zinc oxide elements caused by contamination of the surface of a porcelain bushing as less as possible is not realized, the higher performance of the insulator type arrester has been feared.
Also in a tank type arrester, it has been feared, similarly, due to the rise in zinc oxide elements when a surge of the zinc oxide elements is absorbed, of higher performance of the arrester and achievement of compactness of the arrester resulting from reduction in a using volume of the zinc oxide elements.
That is, in the case where conventional zinc oxide elements of 200 V/mm are used, for example, in an insulator type of 266 kV, about 95 zinc oxide elements are laminated. On the other hand, in the case where zinc oxide elements of high pressure resistance are used, for example, and in the case where zinc oxide elements of approximately 400 V/mm are used, about 48 zinc oxide elements are laminated; and in the case where zinc oxide elements of approximately 300 V/mm are used, about 63 zinc oxide elements are laminated, by which the number of zinc oxide elements can be reduced as compared with prior art.
However, in a state that the number of zinc oxide elements is reduced, a voltage distribution between the zinc oxide elements is affected by grounded electrostatic capacity and becomes uneven, posing a problem in high voltage life characteristics. It is contemplated that a length of a porcelain bushing is shortened to improve the potential distribution between zinc oxide elements. However, since an external creeping flashover occurs considering contamination conditions outdoor, the above length cannot be shortened recklessly. In designing an insulator type arrester, a porcelain bushing contamination resistant voltage and an optimal arrangement of zinc oxide elements are essential.
It is a first object of the present invention to provide an insulator type arrester capable of suppressing a rise in temperature of zinc oxide elements caused by contamination of a porcelain bushing surface. A second object of the invention is to provide an insulator type arrester capable of suppressing a rise in temperature of zinc oxide elements caused by contamination of a porcelain bushing surface, and of achieving higher performance resulting from reduction in a limit voltage. A third object of the invention is to provide an insulator type arrester capable of suppressing a rise in temperature of zinc oxide elements caused by contamination of a porcelain bushing surface, of achieving higher performance resulting from reduction in a limit voltage, and of providing an arrangement wherein a voltage distribution between zinc oxide elements is not uneven by being affected by a grounded electrostatic capacity. A fourth object of the invention is to provide a high performance tank type arrester capable of achieving higher performance of an arrester and reduction in a volume of zinc oxide elements to be used similarly to the insulator type arrester.
A first insulator type arrester according to the present invention for achieving the aforementioned first object comprises an insulting rod provided within a porcelain bushing, a laminate body in which a plurality of metal plates having a thickness greater than a single zinc oxide element does are laminated on upper and lower ends of zinc oxide elements through the insulating rod, a conductor made of metal provided on the lower end of the laminate body, and a resilient member provided on the upper end of the laminate body to press the laminate body into the porcelain bushing.
A second insulator type arrester according to the present invention for achieving the aforementioned second object comprises an insulting rod provided within a porcelain bushing, a laminate body in which a plurality of metal plates are laminated on upper and lower ends of zinc oxide elements through the insulating rod, a conductor made of metal provided on the lower end of the laminate body, and a resilient member provided on the upper end of the laminate body to press the laminate body into the porcelain bushing, wherein the zinc oxide elements have characteristics of an operation starting voltage of 280 V/mm to 500 V/mm.
The zinc oxide elements are featurized by comprising zinc oxide particles, and a grain boundary of a metal additive composed of bismuth oxide, antimony oxide, cobalt oxide, manganese carbonate, chromium oxide, nickel oxide, boron oxide, magnesium carbonate, silver oxide, silicone oxide, and aluminum nitrate. Furthermore, the zinc oxide elements comprise zinc oxide particles of particle size of 1 to 5 xcexcm, and particle size of 0.05 to 0.6 xcexcm of a metal additive composed of bismuth oxide, antimony oxide, cobalt oxide, manganese carbonate, chromium oxide, nickel oxide, boron oxide, magnesium carbonate, silver oxide, silicone oxide, and aluminum nitrate, thus emerging the characteristics of an operation starting voltage of 280 V/mm to 500 V/mm.
A third insulator type arrester according to the present invention for achieving the aforementioned third object comprises an insulting rod provided within a porcelain bushing, a laminate body in which a plurality of metal plates are laminated on upper and lower ends of zinc oxide elements through the insulating rod, a conductor made of metal provided on the lower end of the laminate body, and a resilient member provided on the upper end of the laminate body to press the laminate body into the porcelain bushing, wherein the zinc oxide elements having characteristics of an operation starting voltage of 280 V/mm to 500 V/mm, and the metal plate has a thickness greater than a single zinc oxide element. Alternatively, the metal plate may be divided into a plurality of plates having a thickness smaller than a single zinc oxide element does.
Further, in arranging the metal plates having a thickness larger than a single zinc oxide element does, metal plates increased in thickness by two times, three times, or n times greater than that of the zinc oxide element are arranged stepwise on the lower ends of the zinc oxide elements along the grounded side while adapting to a voltage distribution of an arrester.
A fourth tank type arrester according to the present invention for achieving the aforementioned fourth object comprises a metal shield and an insulating rod provided within a tank, a laminate body in which a plurality of metal plates are laminated on upper and lower ends of zinc oxide elements through the insulating rod, a conductor made of metal provided on the lower end of the laminate body, and a resilient member provided on the upper end of the laminate body to press the laminate body into the tank, wherein the metal plate has a thickness equal to that of a single zinc oxide element in the metal shield portion where an electric field is severe (a portion in which a voltage distribution rate is in excess of 1.0) as shown in a potential distribution of the tank type arrester in FIG. 13, and the metal plates increased in thickness by two times, three times, or n times greater than that of the zinc oxide element are arranged stepwise on the grounded side.
In the first, second and third arresters, the ratio between 10 kA and the operation voltage in the limit voltage characteristics is in the range of 1.9 to 2.4.